Server/DC version of Reminders app is in the Atlassian Marketplace for years. Cloud version is just released and has some missing features compared to server/DC version. Some of these limitations are caused by limitations of Atlassian’s Forge platform and some of them are not implemented yet. Following are main differences you should be aware of when migrating from server/DC version of this app to Cloud version.
Resolution of reminders for server/DC version is in minutes. Cloud version only allows you to select hours and there can be an hour delay when sending reminder e-mails. Currently forge only allows scheduled tasks to be run at hourly intervals. This limitation will be removed in a future version of Forge Platform.
You can't send reminders to “project roles” and direct e-mail address in cloud version of the app.
There is no “My Reminders” page for cloud version. We will add this for next version of the app.
There is no JQLs for finding issues with reminders. Currently this is not possible with Forge Platform.